On energy stable, maximum-principle preserving, second order BDF scheme with variable steps for the Allen-Cahn equation
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In this work, we investigate the two-step backward differentiation formula (BDF2) with nonuniform grids for the Allen-Cahn equation. We show that the nonuniform BDF2 scheme is energy stable under the time-step ratio restriction r_k:=τ_k/τ_k-1<(3+√(17))/2≈3.561. Moreover, by developing a novel kernel recombination and complementary technique, we show, for the first time, the discrete maximum principle of BDF2 scheme under the time-step ratio restriction r_k<1+√(2)≈ 2.414 and a practical time step constraint. The second-order rate of convergence in the maximum norm is also presented. Numerical experiments are provided to support the theoretical findings.
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